Precision cutting instruments that promote accuracy are necessities in surgical procedures. For example, consider total knee arthroplasty. Total knee arthroplasty involves the replacement of portions of the patella, femur and tibia with artificial components. During the procedure, a proximal portion of the tibia and a distal portion of the femur are cut away (resected) and replaced with artificial components. The posterior surface of the patella may also be resected and resurfaced. As used herein, when referring to bones or other body parts, the term “proximal” means closest to the heart and the term “distal” means more distant from the heart. When referring to tools and instruments, the term “proximal” means closest to the practitioner and the term “distal” means distant from the practitioner.
There are several types of knee prostheses known in the art. One type is sometimes referred to as a “resurfacing type”. In these prostheses, the articular surface of the distal femur and proximal tibia are “resurfaced” with respective metal and plastic condylar-type articular bearing components. During primary knee replacement, these knee prostheses require minimal and precise bone resection to accommodate the components within the boundaries of the available joint space.
Often, due to normal wear over time, the prosthetic knee must be replaced via a procedure known as revision surgery. One method for accomplishing revision arthroplasty involves the use of several cutting blocks which may be aligned with reference to the IM canal.
During revision surgery, after the primary prosthetic is removed, the medullary canal is reamed and an intramedulary rod or the reamer itself is tapped in place with a mallet. A distal resection guide is attached to the reamer or the intramedulary rod and distal resection is completed via slots in the guide. The distal resection guide is removed from the rod or reamer and another cutting block is attached for the typical anterior-posterior resection and the anterior and posterior and chamfer resections.
The rotational alignment of the femoral component is critical to ensure correct patellar tracking. Since the posterior condyles are no longer present, this cutting block must be carefully aligned relative to the femoral epicondyles where the collateral ligaments are attached.
After anterior/posterior and chamfer resections are completed, if the posterior cruciate ligament is being sacrificed, the cutting block is removed and a fourth cutting block is attached to the reamer or rod in order to accomplish an intercondylar box resection. Of course, the box resection guide can be incorporated into the same guide used to make the A/P and chamfer cuts.
Following preparation of the femur, similar procedures are performed on the proximal tibia. For example, a reamer or intramedulary rod is installed with a mallet. Preferably, a resection block is pinned to the anterior tibia and a proximal portion of the tibia is resected.
It will be appreciated that given the use of multiple cutting blocks in the described procedure the design of each device should not also add to the complexity of the operation. Generally, such cutting blocks used in surgical procedures may be characterized as open or slotted. In an open block, one surface serves as an open face guide to rest or ply a cutting instrument. In contrast, a slotted block provides an envelope, or “slot” having multiple surfaces within which the block captures the cutting tool or blade to help maintain the blade tracking straight or in desired configuration or arrangement during cutting through the envelope or slot.
In theory, open face blocks induce a greater margin of error than slotted blocks since it is more dependent on surgeon skill to maintain the cutting tool aligned with the guiding surface (e.g., keeping the blade flat against the block). Moreover, a substantially open cutting block may be easier to clean or sterilize when compared to a slotted block. Nevertheless, whether an open face or slotted cutting block is used during surgery is a matter of surgeon preference. To accommodate physician preference it may be appropriate for a medical institution or hospital to have both types of blocks available for the many different procedures for which blocks are designed. However, a drawback of having both slotted and open-face blocks is that it doubles the inventory required to meet the institution's needs. This means more sterilization procedures, more storage issues and ultimately higher costs.